The present invention relates generally to systems for determining the pressure of exhaust gas produced by an internal combustion engine, and more specifically to such systems for estimating engine exhaust pressure as a function of one or more engine operating parameters.
When combustion occurs in an environment with excess oxygen, peak combustion temperatures increase which leads to the formation of unwanted emissions, such as oxides of nitrogen (NOx). This problem is aggravated through the use of turbocharger machinery operable to increase the mass of fresh air flow, and hence increase the concentrations of oxygen and nitrogen present in the combustion chamber when temperatures are high during or after the combustion event.
One known technique for reducing unwanted emissions such as NOx involves introducing chemically inert gases into the fresh air flow stream for subsequent combustion. By thusly reducing the oxygen concentration of the resulting charge to be combusted, the fuel burns slower and peak combustion temperatures are accordingly reduced, thereby lowering the production of NOx. In an internal combustion engine environment, such chemically inert gases are readily abundant in the form of exhaust gases, and one known method for achieving the foregoing result is through the use of a so-called Exhaust Gas Recirculation (EGR) system operable to controllably introduce (i.e., recirculate) exhaust gas from the exhaust manifold into the fresh air stream flowing to the intake manifold valve, for controllably introducing exhaust gas to the intake manifold. Through the use of an on-board microprocessor, control of the EGR valve is typically accomplished as a function of information supplied by a number of engine operational sensors.
While EGR systems of the foregoing type are generally effective in reducing unwanted emissions resulting from the combustion process, a penalty is paid thereby in the form of a resulting loss in engine efficiency. A tradeoff thus exists in typical engine control strategies between the level of NOx production and engine operating efficiency, and difficulties associated with managing this tradeoff have been greatly exacerbated by the increasingly stringent requirements of government-mandated emission standards.
In order to achieve the dual, yet diametrically opposed, goals of limiting the production of NOx emissions to acceptably low levels while also maximizing engine operational efficiency under a variety of load conditions, substantial effort must be devoted to determining with a high degree of accuracy the correct proportions of air, fuel and exhaust gas making up the combustion charge. To this end, accurate, real-time values of a number of EGR system-related operating parameters must therefore be obtained, preferably at low cost. Control strategies must then be developed to make use of such information in accurately controlling the engine, EGR system and/or turbocharger. The present invention is directed to techniques for determining some of these parameters.
In accordance with one aspect of the present invention, a system and method are provided for estimating engine exhaust pressure as a function of other engine operating conditions. In one embodiment, the engine exhaust pressure estimate may be used by itself to supply engine exhaust pressure information to one or more control strategies. In another embodiment, the engine exhaust pressure estimate may be used to validate and/or diagnose the operation of a physical exhaust pressure sensor.
In accordance with another aspect of the present invention, a system and method are provided for estimating intake air pressure as a function of other engine operating conditions. In one embodiment, the intake air pressure estimate may be used by itself to supply intake air pressure information to one or more control strategies. In another embodiment, the intake air pressure estimate may be used to validate and/or diagnose the operation of a physical intake air pressure sensor.
These and other objects of the present invention will become more apparent from the following description of the preferred embodiments.